Ball chair



FIG. 1 is a perspective view of the ball chair showing my new design;

FIG. 2 is a front elevational view thereof;

FIG. 3 is a rear elevational view thereof;

FIG. 4 is a left side view thereof;

FIG. 5 is a right side view thereof;

FIG. 6 is a top plain view thereof; and,

FIG. 7 is a bottom plain view thereof. 

The ornamental design for a ball chair, as shown. 